1. Field
This disclosure is concerned generally with anthelmintic preparations and specifically with a single, easy-to-administer preparation useful in eliminating common helminths including both nematodes and cestodes from carnivores, especially domesticated animals such as dogs and cats.
2. Prior Art
The term anthelmintics is used to describe a broad class of compounds useful for expelling or destroying parasitic worms, especially those found in the intestine. Depending of the specific anthelmintic compound, the action against the worms will be either primarily systemic or primarily via direct contact with the worms in the gastrointestinal tract of the afflicted animal. In general, the type of anthelmintic to be used will depend on the class or classes of worms to be eliminated.
In the case of larger animals such as cattle and horses, such anthelmintics have been simply mixed with the animals' feed ration in the form of a powder, granules, suspension or, more recently, as a paste which, due to its tacky nature, will adhere to the grain parts. Such tackiness not only assures that the anthelmintic will in fact be ingested by the animal, but also assures an anthelmintically effective direct contact with worms as the grain/anthelmintic paste passes through the gastrointestinal tract. Examples of such anthelmintic pastes can be found in U.S. Pat. No. 3,746,490 to Marsland et al (resin based formulation of the liquid dimethyl-2,2-dichlorovinyl phosphate or DDVP), U.S. Pat. No. 4,141,975 to Gay et al (mineral oil based formulation of trichlorfon) and U.S. Pat. No. 4,277,467 to Dorn et al (trichlorfon and febantel in a paste formulation having a water content of less than 1% by weight).
A broad spectrum anthelmintic for carnivores, unlike those developed for farm animals and horses, must concern itself with both nematode (roundworm) and cestode (flatworm or tapeworm) parasites. Cestodes have not routinely been perceived as a serious economic problem in food animals or of sufficient incidence in horses to warrant product development. These different classes of parasites have frequently required separate medications or combinations of medications to achieve their degree of success. These products in carnivores, especially domesticated dogs and cats, have all had their shortcomings. Vermiplex.TM. anthelmintic, like similar products from other manufacturers, is a combination oil-based capsule for dogs and cats. It is difficult to administer, particularly to cats, and is marginal in efficacy particularly with respect to cestodes. A paste product (Felex#) is available for cats in Australia, but its activity is limited to nematodes. For dogs, there is a powder formulation of mebendazole (Telmintic.TM.) available, but it is essentially ineffective against Dipylidium caninum, a common cestode in dogs. Also, its efficacy is dependent on successful administration through mixing in the food.
Attempts to formulate a broad spectrum (i.e. covering all common nematodes and cestodes) yet easy-to-administer anthelmintic preparation for carnivores have been difficult and to date unsuccessful. To assure a broad spectrum action, it would apparently be necessary to somehow combine anthelmintics which are on the one hand primarily systemically active with, on the other hand, anthelmintics which are active against helminths primarily via direct contact in the carnivore gut (or gastrointestinal tract). In general, the best system for the base would be a formulation that would provide for maximum anthelmintic response of both the active components and also one in which both active ingredients were stable. The one agent, primarily systemic in nature, should be given in a form that is readily available for absorption from the gut into the carnivore blood stream. A systemically active anthelmintic known as praziquantel (DRONCIT.RTM. anthelmintic, Bayvet Division, Cutter Laboratories, Inc., Shawnee, Kan.), is known to be effective against cestodes (tapeworms). See Kruckenberg, S. M. et al, "Preliminary Studies of the Effects of Praziquantel Against Tapeworms in Dogs and Cats", VM/SAC 77:689-692, 1981.
Among the anthelmintics known to be effective against worms via direct contact in the gut is febantel (see U.S. Pat. No. 3,993,682 to Kolling et al). In general, such anthelmintics do not dissolve completely in water and this partial insolubility and the poor absorption by the gastrointestinal tract tends to assure their direct-contact action against certain intestinal worms. Because of their limited solubility, such anthelmintics may be administered in the form of a suspension of fine particles or in a paste-like form which can be administered in the food. In paste applications, the particle size of the anthelmintic compound is commonly controlled to assist in paste formation (see U.S. Pat. No. 4,141,975 cited above) and in dispersion of particles in the formulation to assure anthelmintic activity. Other anthelmintic pastes are disclosed in an article by R. M. Corwin et al, Am. J. of Vet. Res., Vol. 43, No. 6, pp. 1100-1102, 1982 (febantel paste) and the articles cited therein (febantel/trichlorfon paste).
Since the direct-contact anthelmintics do not rely on water solubility for their administration, it has been common practice to use as a vehicle an inert organic liquid such as mineral oil to assist in particle dispersion, paste formation and product stability. Thus, water has been avoided or minimized in these products and, in the case of a recent combination paste of two anthelmintics (trichlorfon and febantel), it is a requirement that the water content, if any, be less than 1 percent by weight of the paste. Unfortunately, by limiting the water content (e.g. to assure long term stability), it becomes difficult to formulate certain water-soluble systemically active anthelmintics with other direct contact anthelmintics to obtain a relatively broad spectrum anthelmintic product.
We have found that it is possible to prepare a stable, relatively broad spectrum anthelmintic composition by choosing a vehicle which simultaneously provides systemic and direct contact availability for both systemic and direct contact anthelmintic drugs when in a carnivore gut. Details of the anthelmintic composition are described below.